Patent Document 1 discloses a technology in which in a vehicle equipped with a plurality of batteries having different voltages, the battery for which the maximum generation power of an alternator determined by its rotation speed and voltage is relatively highest is selected to be charged.
Patent Document 2 discloses a technology in which in a vehicle equipped with a plurality of batteries having different voltages, a battery to be charged is selected based on the state of charge (SOC) of the batteries.